Coaxial attenuators are too bulky and expensive to be implemented on many microwave systems. Distributed ferrite load material on transmission lines have difficulty in realizing repeatable and precise attenuation values because of inconsistencies in the manufacturing the bulk material. Couplers on airstripline are not practical to realize small and precise attenuation values because of difficulties in match due to the unequal even and odd modes association with that type of transmission line.
Typical lumped element attenuator configurations utilize at minimum three resistors. Each resistor value should be held to very tight tolerances, e.g. on the order of 1% or better. Often active laser trimming is employed to achieve these precise resistor values. Laser trimming is typically preformed on printed resistor-on-ceramic substrates. This operation is prohibited for many large microwave printed circuit boards using non-ceramic material (Teflon® for example) because of the risk of damaging the board by the laser.